1. Field of the Invention
The invention relates to an ablation device for cardiac tissue, in particular for forming a circular lesion around a vessel orifice in the heart, comprising a catheter which, in the region of its distal end, is provided with an abutment device for holding the distal end on a cardiac vessel orifice.
2. Background Art
Regarding the background of the invention it can be stated that catheter ablation is a therapy that is used to an increasing degree to treat certain types of arrhythmia. In the process, a lesion—i.e., a denaturation of tissue along the line of a tissue scarring—is created with the aid of the ablation applicator of the catheter at a certain location in the myocardial tissue in order to sever the faulty electrical stimulus pathways at that location that are responsible for arrhythmia. The introduction of energy into the myocardial tissue via the ablation applicator, as a rule, takes place by means of ablation electrodes that operate with high-frequency current. Other forms of energy, such as microwave energies, high-energy direct current or, in principle, other denaturing mechanisms, such as freezing or chemicals (for example alcohol), may also he used for the ablation. The term “ablation applicator”, as it is used in the present application also in connection with the subject matter of the invention, shall always mean all of the listed ablation options, with ablation electrodes representing the most common variant.
From a multitude of ablation catheter variants that are adapted to their respective purposes, WO 98/49957 A1, which discloses an ablation device for generating linear lesions between the orifice openings of two pulmonary veins into the atrium of the heart, has been selected as the prior art. According to the preamble of claim 1, a steerable catheter is provided, which carries, on its distal end, an abutment device in the form of a dilatable balloon to secure the catheter in the ostium of the pulmonary vein.
In this known ablation device the catheter serves not only for basic positioning of the ablation applicator, but it also carries, on its shank, the given ablation electrodes themselves. In this special design, the catheter shank, proximally relative to the ablation electrodes, can now be brought to the front of the orifice opening of a second pulmonary vein by means of a second guide so that the linearly aligned ablation electrodes come to rest on the connecting line between the two orifice openings of two adjacent pulmonary veins. In this manner, a linear lesion can reliably be applied between the two orifice openings.
Further embodiments of ablation catheters are for example shown in U.S. Pat. No. 5,239,999 A, WO 95/15115 A1 and WO 95/31111 A1, which disclose ablation electrodes in variably coiled or slightly bent shape.
Recent studies have shown that circular lesions around or at the orifices of the pulmonary veins (hereinafter: pv orifice) into the atrium have been successful, especially for treating the atrial fibrillation of the heart.
The known ablation devices are not practical for lesions of this shape, there being no or hardly any possibility of putting into practice an annular arrangement of the ablation electrodes around or at the pv orifice.